In the quest for oil and gas, operators are continually searching for devices and methods for drilling wells faster and more economically. Traditionally, a drill bit is attached to a drill string, which is rotated to cause the drill bit to rotate, and hence, bore through the earth to drill a well. Over the years, various types of drill bits and drill strings have been developed to facilitate the formation of inclined and/or directional well bores.
Drilling into rock or other types of hard formations requires relatively large power levels and forces that are usually provided, at the drilling rig, by applying a torque and an axial force through a drill string to a drill bit. When drilling a vertical wellbore, for example, the lower portion of the drill string (e.g., the bottom hole assembly (BHA)), typically includes (from the bottom up) the drill bit, a bit sub, one or more stabilizers and/or drill collars, heavy-weight drill pipe, jarring devices, and crossovers for various thread forms. The BHA provides force, the measure of which is referred to as “weight-on-bit,” to penetrate through rock or other hard materials.
Directional drilling operations require directional control to position the drill bit, and thus the well, along a particular trajectory in a formation. Directional control has traditionally been accomplished using special BHA configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface, mud motors, rotary steerable systems, and other specialized BHA components and drill bits adapted for this purpose. Conventionally, a directional driller can also use drilling parameters, such as weight-on-bit and rotary speed, and drilling tools to attempt to deflect the bit away from the current axis and/or trajectory and onto the desired path.
A typical directional drill string may contain a BHA which includes: a bit, a bent sub, a drilling motor, and one or more measurement-while-drilling, surveying, and/or logging tools. When using this type of BHA, the drill string is ideally held stationary with respect to rotation. The drilling motor generates rotation of the bit via circulation of the drilling fluid through the drilling motor. While the drill string is held stationary with respect to rotation, the well builds or reduces angle in a controlled manner as a function of the degree of bend in the bent sub.
Directional control can theoretically be accomplished through the use of a bent sub located near the bit, in which the bend within the sub orients the bit toward a direction that deviates from the axis of the wellbore when the drill string is not rotating. By pumping mud through the mud motor, the bit rotates, even when the drill string itself does not, allowing the bit alone to rotate and drill toward the direction of the bend in the bent sub. When a desired wellbore direction is achieved, the new direction may be maintained by permitting the drill string, including the bent section, to rotate, such that the drill bit bores in a generally straight direction, parallel to the current axis of the wellbore. As it is well known by those skilled in the art, however, a drill bit rotated by a mud motor has a tendency to stray from its intended drilling direction—a phenomenon known as “drill bit walk.” Drill bit walk results from the cutting action, gravity, and rotation of the drill bit, as well as irregularities within the formation being drilled. It is desirable to eliminate, or at least minimize, drill bit walk to ensure drilling proceeds in the desired direction, thereby producing less tortuous well paths and improving drilling operation efficiency and success.
Drill bit walk, a common problem encountered when using directional drilling assemblies, is the result of the reactive torque generated by the bit. The bit torque generates an equal and opposite reactive torque that is transferred from the motor into the bottom hole assembly and drill string, causing the BHA and string to counter-rotate relative to the bit. Further, the reactive torque, and hence the drill string counter-rotation, can vary due to drilling conditions, such as the weight-on-bit, properties of the formation being drilled, and hole condition, all of which vary independently of each other. Because the bent sub is part of the BHA being counter-rotated, the direction, in which the well is being drilled, changes concurrent with changes in reactive torque, resulting in the drill bit walk phenomenon described above.
As a result of reactive torque induced drill bit walk, a driller is typically required to make numerous surface adjustments of the drill string, and hence the bent sub, to maintain a desired drilling direction. These numerous adjustments are subject to error, cost valuable rig time, and reduce the efficiency of the drilling operation. Additionally, directional drillers may attempt to employ measurement while drilling and rotary steerable systems to periodically correct deviations caused by drill bit walk, each of which adds expense and complexity to the downhole assembly, thus raising the cost of the drilling operation and increasing the possibility of a downhole equipment failure. By eliminating, or greatly reducing, the net reactive torque on the BHA and drill string, drilling can proceed unabated in the desired direction, saving time and expense. When drillers are able to eliminate, or reduce, net reactive torque on the BHA and drill string, they become able to use more powerful motors and more weight-on-bit to increase drilling rates of penetration and can create smoother, less tortuous boreholes for running logging tools and setting casing.
Some existing drilling devices incorporate an inner drill bit used to bore through a formation and an outer drill bit or a reamer used to smooth and/or enlarge the initial borehole. However, due in part to the differing diameters of such components, the rotational speed of each drill bit or reamer is different, which causes the drilling penetration rates of each bit or reamer to differ, creating unstable drilling progress as one bit drills ahead of the other, and reduces the overall rate of penetration of the drill due to the slower turning bit or reamer. Additionally, existing pilot-reamer systems contain bits which drill in the same direction, thereby transmitting a net reactive torque to the drill string during operations causing drill bit walk.
Therefore, there is a need for a drilling assembly that can be steered more quickly and accurately than conventional directional drilling assemblies.
In addition, there is a need for a device and methods usable to reduce the net reactive torque experienced by a BHA, mud motor, drill string and/or other components while drilling wells.
A need exits for a device and methods of use that will enable a faster and more efficient drilling of wells.
In addition, a need exists for a device that will transfer torque from the drilling motor to counter-rotating inner and outer drilling bits.
Further, there is a need for a device and method of use that will enable the counter-rotating of inner and outer bits, to be rotated at the same rotational speed. There is also a need for a device and methods of use that will enable the counter-rotating of inner and outer bits, to be rotated at different rotational speeds.
The present invention meets all of these needs.